Polyimide precursors

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

Photosensitive functions are in many cases also heat sensitive, so the preparation of photosensitive polyimides needs smooth conditions for the condensations and imidization reactions. Some chemical reactants, which can be used for polyamide preparation, have been patented for the synthesis of polyimides and polyimide precursors. For example, chemical imidization takes place at room temperature by using phosphonic derivative of a thiabenzothiazoline.102 A mixture of N -hydroxybenzotriazole and dicyclohexylcarbodiimide allows the room temperature condensation of diacid di(photosensitive) ester with a diamine.103 Dimethyl-2-chloro-imidazolinium chloride (Fig. 5.25) has been patented for the cyclization of a maleamic acid in toluene at 90°C.104 The chemistry of imidazolide has been recently investigated for the synthesis of polyimide precursor.105 As shown in Fig. 5.26, a secondary amine reacts with a dianhydride giving meta- and para-diamide diacid. The carbonyldiimidazole... 

Polymer Synthesis and Modification. The condensation reaction between either BTDA or BDSDA and ODA was performed in DMAc at room temperature under a nitrogen atmosphere. ODA (0.004 mole) was added to a nitrogen-purged glass septum bottle with 7 ml DMAc. One of the dianhydrides (0.004 mole) was then added to the diamine solution with an additional milliliter of DMAc resulting in 15-25 wt% solids depending upon the monomer combination. The resulting solution was stirred for 20-24 hours to form the poly(amide acid), a polyimide precursor. For the modified polyimides, anhydrous cobalt(II) chloride (0.001 mole) was added as a solid within one-half hour after the dianhydride. 

As illustrated in Scheme 6, monosilylation of the aliphatic diamine nitrogen atoms and subsequent reaction with the dianhydride yields a polyimide precursor devoid of free carboxylic acid groups, a poly(amic trimethylsilyl ester)... 

The solution behavior of poly(amic acids) was until recently, probably the least understood aspect of the soluble polyimide precursor. However, the advent of sophisticated laser light scattering and size exclusion chromatography instrumentation has allowed elucidation of the solution behavior of poly(amic adds). In the early days of polyimide chemistry, when most molecular weight characterization was based on viscosity determinations, a decrease in viscosity was associated with molecular weight degradation [15, 28, 29]. Upon combination of the two monomers an increase in the viscosity to the stoichiometric equivalence point is observed, followed by a decrease in the solution viscosity as a... 

Poly(amic acids) in which the ortho-carboxylic group has been chemically modified to either an ester- or amide moiety have been known for many years. However, their commercial significance was non-existent until very recent applications involving dielectric insulators [48] and photosensitive polyimide precursors [49, 50]. As with many synthetic pathways, there are generally several ways to arrive at the same goal. Similarly, the preparation of derivatized poly(amic acids) can be divided into two general categories ... 

Fig. 7. Polymer solution stability of pyromellitic dianhydride/aniline phthalein based polyimide precursor in dimethylacetamide at ambient temperature. [C] = 0.5 wt%, ( ) poly(amic methyl ester), ( ) polyfamic acid) [66]...

Initial investigations of base-catalyzed imidization of polymeric systems, in particular PMDA/ODA based polyfamic alkyl esters), have been difficult due to the insolubility of the polyimide precursor at imidization levels exceeding 40%. Nevertheless, preliminary studies indicate that the base-catalyzed polymer imidization reaction appears to be significantly slower at ambient temperatures as compared to the phthalamide model compounds. It is yet unclear whether this is a direct result of the conformational aspects associated with the polymer chain or solubility considerations arising from the less soluble, partially imidized polymer chain. Since much of the initial work involved IR studies of supported... 

Of course, this re-equilibration behavior of two homopoly(amic acids) can be eliminated if one of the components does not exhibit this back reaction. Recombination of different fragments is not possible and stable polyimide precursor blends are accessable [119]. For example, combining a relatively flexible poly(amic acid), hexafluoroisopropylidene diphthalic anhydride (6F)/2,2-bis(4-aminophenoxy-4 -phenyl) propane (BDAF), with a rigid poly(amic alkyl ester), PMDA/p-phenylene diamine (PDA), produced microphase separated polyimide blends as can be interred by the persistence of the... 

Polyimides. In situ co-deposition of metal salts such as Co(II), or LiCl into a polyimide precursor from 3,3, 4,4 -tetracarboxybenzophenone dianhydride and 4,4 -diaminobenzophenone with subsequent thermal curing offers surface-conductive polyimide film [43]. By similar procedures, Taylor et al. prepared a series of polyimides modified with Pd, Pt, Ag, Au, Cu, Sn, Ti and magnetic-Fe [44, 45, 46]. 

Copper has been the most widely used material because of its high conductivity, solderability, low cost, and ability to be electrolytically or chemically plated. However, copper has a weak interaction with polyimides (102-104) and, consequently, poor adhesion. Furthermore, recent studies have shown that the polyimide precursor, polyamic acid, oxidizes copper... 

Takeichi, T., Eguchi, Y., Kaburagi, Y., Hishiyama, Y., Inagaki, M. (1999) Carbonization and graphitization of BDPA/PDA polyimide films effect of structure of polyimide precursor, Carbon 37(4), 569-575. 

Title Diamines, Polyimide Precursors, and Polyimides Produced by Using the Diamines and Liquid Crystal Aligning Agents... 

A reaction flask was charged with 3,5-di-dodecyloxybenzyl-3,5-diamino-benzoate-diamine (0.75 mmol), 1, 2, 2 -bis[4-(4-aminophenoxy)phenyl]propane (4.25 mmol), 1,2,3,4-cyclobutane tetracarboxylic dianhydride (5.00 mmol), and A-methylpyrrol-idone (17.69 g) and then stirred at ambient temperature until a 15 wt% solid content polyimide precursor solution was obtained. 

Materials. The polyimide precursor used was DuPont PI5878 poly(amic acid) and is based on PMDA-ODA. N-methylpyrrolidinone (Aldrich M7960 3) (NMP) was used as the solvent. 

---